The invention relates to a device for delivering any one of a plurality of gases to an apparatus, especially a trace-impurity analyzer such as an atmospheric-pressure ionization mass spectrometer.
In the field of the analysis of very-high pure gases, it is increasingly necessary to analyze using the same analyzer, sequentially and with a short switching time, gases coming from various sampling lines.
In this case, the gases contained in the sampling lines may be of various kinds, or may be of the same kind but sampled at various points in a plant, for example in a plant for fabricating semiconductor components.
A gas delivery device is known in which each sampling line is connected to a common gas delivery line which itself is connected to the analyzer. A shut-off valve is placed in each of the sampling lines.
In order to select a gas to be analyzed, which comes from a particular sampling line, the shutoff valves of the other sampling lines are closed and only the valve in the sampling line selected is switched to the open state.
This known system has the drawback that the flow stagnates in the blocked sampling lines, which causes undesirable interactions with the walls of the pipe of the line, such as desorption or adsorption phenomena, for example.
In addition, this known device has, downstream of the shutoff valves, flow-stagnation volumes in which gases accumulate. Each time a switch is made from one sampling line to another and consequently each time the gas to be analyzed is changed, the gases which have accumulated in these flow-stagnation volumes contaminate the new gas to be analyzed, and a considerable amount of time is required to remove them. It may therefore be understood that it is impossible to pro-duce short switching times with such a gas delivery device.
The present invention aims to alleviate these various drawbacks by providing a gas delivery device which does not have a flow-stagnation volume in the common gas delivery line, which allows continuous purging of each of the sampling lines and rapid switching from one gas to be analyzed to another, while still ensuring that the gases conveyed to the analyzer are rapidly representative.
To this end, the subject of the invention is a device for delivering any one of a plurality of gases to an apparatus, comprising at least two valves each connected, on the one hand, to a respective gas sampling line and, on the other hand, to a common line for delivering gas to the apparatus, characterized in that each valve comprises a first conduit permanently connected via one end to the respective sampling line and via its other end to a respective purge line, a second conduit and an actuator which can be switched between a position for bringing the first conduit into communication with the second conduit and a position for isolating the first conduit from the second conduit, at least the second conduit being free of flow-stagnation volumes, the second conduits of the valves are placed in series in the common gas delivery line, the end of this common line, opposite said apparatus, emerging in an additional purge line and each purge line passes through an element for creating a pressure drop.
The device according to the invention may include one or more of the following characteristics:
the second conduit of each valve includes a chamber in which emerges at least one conduit connecting the first conduit to said chamber and each valve includes a closure element on which the actuator of the valve acts, which closure element, in said isolating position, closes off the end of the connecting conduit emerging in said chamber and which is set back with respect to this end of the conduit in said communicating position;
the end of the connecting conduit emerging in said chamber is provided with a seal projecting into the chamber and the closure element comprises an elastically deformable diaphragm forming part of the wall of the chamber opposite the seal, the diaphragm being pressed in a sealed manner onto the seal against the spring force of the diaphragm, in said isolating position, by a pusher of the actuator;
each purge line includes a respective element for creating a pressure drop;
all the purge lines are connected, downstream of the elements for creating a pressure drop, to a common evacuation line;
the sampling lines and the additional purge line each include an element for creating a pressure drop, the purge lines associated with each valve are joined into a common purge line, the common purge line includes a diverter for setting a constant pressure in the common gas delivery line;
at least one element for creating a pressure drop is a flow-regulating element;
each flow-regulating element is formed by a gaged orifice;
each valve includes means for controlling the switching of the actuator between said communicating and isolating positions, the means for controlling each valve are connected to a control unit for isolating each valve or for bringing it into communication, and the control unit includes logic means which prevent the simultaneous switching of several actuators in the communicating position.